Methods of encryption are essential for commerce and many other uses to provide secure electronic communications. The history of encryption is an important and fascinating aspect of the history of mankind and even was a driving force for the invention of computers. During World War II, the German armed forces used the famous Enigma Machine, a mechanical substitution encryption device, for secure communications within their army. However, Enigma communications were first broken by Poland and then subsequently, on an ongoing secret basis for over 30 years by the British in their Bletchley Park location, which involved a collection of their top mathematicians including the famous Alan Turing. The Allied D-Day invasion of Normandy only occurred after confirming with secretly decrypted Enigma messages, that the Germans were not aware of the upcoming invasion. Similarly, the Americans, were able to also secretly decrypt secure communications within the Japanese army.
Currently, the most commonly used form of encryption for online communications, public key encryption, is asymmetric encryption. In this form of encryption, a party has a pair of keys. One key is a public key, which can be made freely available to the public. The other key carefully guarded by the party is a private key. A message encoded with the particular public key can only be decoded using the corresponding private key, and vice versa. RSA (Rivest-Shamir-Adleman) is the most commonly used public key algorithm. The mathematical problem of determining the prime composite factors of large numbers (e.g. 100-200 digit numbers) limits decryption by unauthorized parties. The drawback with such methods is that the private keys can be deciphered with sufficient effort (as was done in 1994 by 600 volunteers and their computers), and if an unauthorized party gains knowledge of the private key, then the encrypted messages are readily decrypted.
In symmetric methods of encryption, the sender and the recipient use the same code to encrypt and decrypt the message. For example, the Data Encryption Standard (DES) is a widely used symmetric encryption algorithm which was originally developed by IBM in the mid-1970's. DES is a block cipher with 64 bit block size. It uses 56-bit keys. Many current commerce applications use DES. It can, however, be broken using modern computers and special hardware. Other encryption standards can also be broken by applying a large number of processors since the calculations can be broken down into separate tasks.
The only cipher which cannot possibly be broken or deciphered is the One-Time Pad (OTP), which has been used for secure communication between the heads of the United States and Russia. The first OTP was the Vernam Cipher invented by Gilbert Vernam of AT&T in the United States in 1918. This cipher simply takes a stream of bits that contains the plaintext message, and a secret random bit-stream of the same length as the plaintext (the key). To encrypt the plaintext with the key, each pair of bits from the key and plaintext is sequentially acted on by the exclusive or function to obtain the ciphertext bit. The ciphertext cannot be deciphered if the key is truly random and the key is kept secret from an unauthorized party. The problem with this method is that the key should be at least the same length as the message. If a shorter key is used and repeated then the cipher can be broken. Consequently the problem of securely communicating the random key for each message is just as problematic as securely communicating the message. If an unauthorized party obtains the key, the message is readily decrypted.
After the Enigma Machine, the Lorenz Company used the Vernam Cipher concept in the early 1940's to create their Lorenz machine for the German armed forces to use for even more secure communications. The Lorenz machine was a mechanical attachment to teleprinters which created pseudo-random sequences. An operational mistake made by a German transmitter operator who reused a pseudo-random key to retransmit a message allowed the British Bletchley Park team to better understand the Lorenz machine. Then using about 1,500 vacuum tubes, the Bletchley Park team created the Colossus system in December 1943 to regularly secretly decrypt Lorenz communications. Many believe Colossus to be the first electronic computer, however even its existence was not made known until many years later. All Colossus machines were subsequently destroyed to maintain their secrecy. The problem with Lorenz was that because of mechanical limitations, only pseudo-random keys could be created, not truly random ones. With todaycs usage of electronic computers, truly random keys can now be created.
There is a need therefore for purposes of encrypted messages in situations where extreme security is required for a method of encryption where an unauthorized party cannot decrypt messages in a timely way even with knowledge of the decryption algorithm.